Fan blade assembly for electric fan

ABSTRACT

Fan blade assemblies are provided for quiet and efficient operation in portable electric axial flow fans intended for home or office use. The blades of the fan blade assemblies include a forward sweep to provide relatively quiet operation. The camber lines of the blades are curved to provide generally concave pressure surfaces and generally convex suction surfaces.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of the invention relates to electric fans and blade assembliesfor such fans.

2. Brief Description of the Related Art

Electric fans have a variety of uses and are designed in various ways toprovide desired air flows. Axial flow fans move air substantiallyparallel to the axis of rotation of the fan blade assembly. Theoperating characteristics of axial flow fans can vary significantlydepending on parameters such as blade width and shape and the number ofblades in the assembly.

A number of terms are employed to described the physical characteristicsof axial flow fans. The leading edge is the edge of the blade that firstmeets the air as the blade is rotated. Blades also have trailing edges.The camber line is a line extending through the center or midpoint of ablade between the leading edge and the trailing edge. An axial flow fancommonly has a curved camber line. The camber angle is an angle createdby the intersection of two straight lines tangent to the camber line:one straight line passing through the leading edge and the other passingthrough the trailing edge. The camber angle distribution may besubstantially uniform between the root and the tip of a blade or it maybe variable. The mean camber angle is defined as the average of thecamber angles measured between the root and the tip of the blade.

The chord line of a fan blade is a straight line extending between theleading and trailing airfoil edges. The space between adjacent blades,or pitch, is the distance in the direction of rotation betweencorresponding points on adjacent blades. The solidity is the ratio ofblade chord to the spacing or pitch. Solidity can be increased by addingblades and/or by using blades with a wider chord. Blade load increaseswith decreases in solidity. If the solidity is too low, the airflow fromthe fan may separate. While the pressure capability of a fan increaseswith increasing solidity, skin friction losses will also increase.Solidity should accordingly be considered in designing an effective fanblade assembly.

Loading of a fan as described herein refers to aerodynamic loading.Loading can be defined as the difference in air velocity on the suctionand pressure sides of a blade. A larger difference in velocity on eachside of the blade is associated with a larger difference in staticpressure on each side, leading to additional load. Loading distributionrelates to how the total work provided by a fan blade to the air flow isdistributed by the blade from the leading edge to the trailing edge.Work performed by a fan is related to the number of blades, the bladechord, blade contour, and fan velocity.

Portable electric fans used in homes and offices include a support, anelectric motor mounted to the support and a fan blade assemblyoperatively associated with the motor. The type of support determineswhether the fan is categorized as a table fan, a stand fan or other typeof fan. Most fans of these types are axial flow fans. As they are usedwhere people may be working, listening to music, watching television orengaged in conversation, it is desirable that such fans do not causeexcessive noise. Noise is proportional to fan speed. A fan having arelatively high solidity can produce the same airflow at a lower speedthan an otherwise similar fan having lower solidity. As discussed above,efficiency may, however, be reduced with increasing solidity. There isaccordingly a range of optimal solidity where it is not so high thatskin friction losses render the fan inefficient nor so low that loadingis increased to the extent that airflow stalls and separates.

SUMMARY OF THE INVENTION

The invention relates to fans and fan blade assemblies designed forquiet and efficient operation in homes, offices and similar settings.

In accordance with a first embodiment of the invention, a fan bladeassembly is provided for an electric axial flow fan. The assemblyincludes a hub and plurality of fan blades mounted to the hub forproviding axial flow as the hub is rotated about an axis of rotation.Each blade includes a blade body having an airfoil portion includingradially inner, outer and mid-span portions. The blade body ispreferably substantially uniform in thickness. It includes a leadingedge, a trailing edge, and an outer edge connecting the leading andtrailing edges. The outer edge is shorter in length than the lengths ofthe leading and trailing edges. The blade body further includes apressure surface and a suction surface. The camber line is curved suchthat the pressure surface is generally concave and the suction surfaceis generally convex between the leading and trailing edges. The leadingand trailing edges are curved such that the radially inner portion ofthe airfoil has a rearward sweep with respect to the direct of rotationof the hub and the radially outer portion thereof has a forward sweep.The pressure surface is generally concave and the suction surface isgenerally convex between the hub and the outer edge. The forward sweptangle of the leading edge is preferably greater than 60 degrees and thesolidity is preferably about 0.4 or greater.

A portable fan is provided by the invention, and includes a support, anelectric motor mounted to the support, a fan blade assembly operativelyassociated with the electric motor and a grill at least partiallyenclosing the fan blade assembly. The fan blade assembly includes a huband a plurality of fan blades mounted to the hub. Each blade includes anairfoil portion of substantially uniform thickness and including inner,outer and mid-span portions. The blade body further includes a leadingedge, a trailing edge, an outer edge connecting the leading and trailingedges, a pressure surface, and a suction surface. The pressure surfaceis generally concave and the suction surface is generally convex betweenthe leading and trailing edges. The leading and trailing edges arecurved such that the airfoil radially inner portion is rearward sweptwith respect to the direction of rotation of the hub and the radiallyouter portion is forward swept. The pressure surface is generallyconcave and the suction surface is generally convex between the hub andthe outer edge.

In accordance with a further embodiment of the invention, a fan bladeassembly for an axial flow electric fan is provided that includes a huband a plurality of fan blades mounted to the hub. The blades aredesigned to provide axial air flow as the hub is rotated about an axisof rotation. Each blade includes a blade body having an airfoil portion,a leading edge, a trailing edge, a pressure surface, and a suctionsurface. The blade body further includes a curved camber line whereinthe pressure surface is generally concave and the suction surface isgenerally convex between the leading and trailing edges. The leading andtrailing edges are curved such that the airfoil portion includes aradially inner portion having a rearward sweep and a radially outerportion having a forward sweep with respect to the direction of rotationof the hub. The solidity is preferably about 0.6 or greater.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a fan in accordance with afirst embodiment of the invention;

FIG. 2 is a front elevation view of a fan blade assembly in accordancewith the first embodiment of the invention;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a side elevation view thereof;

FIG. 5 is a rear elevation view of a blade for the blade assembly shownin FIGS. 2-4;

FIG. 6 is an end view thereof;

FIG. 7 is a partially sectional view thereof taken along line 7-7 ofFIG. 5;

FIG. 8 is a graph showing the blade angle (β) distribution of the bladeshown in FIGS. 1-7;

FIG. 9 is a perspective view of a fan blade assembly in accordance witha second embodiment of the invention;

FIG. 10 is a front elevation view thereof;

FIG. 11 is a rear elevation view thereof;

FIG. 12 is a side elevation thereof;

FIG. 13 is a front elevation view of a blade for the blade assembly ofFIGS. 8-11;

FIG. 14 is a perspective view thereof;

FIG. 15 is an end view thereof; and

FIG. 16 is a graph showing the blade angle (β) distribution of the bladeshown in FIGS. 9-15.

DETAILED DESCRIPTION OF THE INVENTION

The description which follows is directed to preferred embodiments ofthe invention. It will be appreciated that the invention is not to beconsidered limited to the preferred embodiments, and that the scope ofthe invention is to be determined in accordance with the appendedclaims.

A portable electric fan 10 according to a first embodiment of theinvention is shown in FIG. 1. The fan includes a support 12, an electricmotor assembly 13 mounted to the support, a fan blade assembly 14operatively associated with the electric motor assembly 13, and a grill16 enclosing the fan blade assembly. The grill includes two halves thatare connected by wing clips 17. A grill nut 15 connects the rear half ofthe grill to the housing for the motor assembly 13. This type of fan 10is known as a stand fan. The support includes a base 18, a longextension pole 19A coupled to the base, and a short extension pole 19B.The short extension pole 19B has a lower end of reduced diameter thatextends within the top end of the long pole 19A. A set screw is employedto lock the poles together. The motor 13 is coupled to the top end ofthe short pole 19B by a bracket 21 A including a neck 21B. The neck 21Bextends into the top end of the short pole 19B and is affixed thereto bya set screw. A weight 23 is mounted to the base 18 to provide stability.

The fan blade assembly 14 is comprised of four identical fan blades 20and a hub 22, as shown in FIG. 2. The hub is comprised of a centerportion 24 and four radially projecting arms 26, as best shown in FIG.3. The center portion 24 includes a cylindrical projection 28 that isaxially aligned with the axis of rotation of the fan blade assembly. Aset screw 30 extends through the wall of the cylindrical projection 28to allow the fan blade assembly to be coupled to the output shaft 31 ofthe electric motor assembly 13. The hub 22 is preferably of integralconstruction and substantially rigid. Each arm has substantially flatinner and outer surfaces. The outer end of each arm has an arcuateconfiguration.

Each arm 26 of the hub is coupled to a blade 20. The flat outer surfacesof the arms 26 adjoin substantially flat inner (suction) surfaces of thefan blades. Rivets 32 are employed for securely affixing the fan blades20 to the arms. A pair of rivets 32 are preferably employed to affix ablade to each arm, one near the inner end of the arm and the other nearthe outer end thereof.

The blades 20 employed in the preferred embodiment are made of aluminumand have a substantially uniform thickness of about 1.0 millimeters.This thickness is not believed to be critical, and any thickness betweenabout 0.8 mm and 1.5 mm should not materially affect performance of thefan blade assembly. The blades may be coated or painted for protectionand/or aesthetic purposes. The radially inner portion 34 of each bladeincludes a substantially flat leading portion while the trailing portionis curved to form a generally concave outer pressure surface. Each bladeinner portion 34 extends from a generally arcuate inner blade edge 36 toa generally arcuate boundary 38 near the outer edge of each hub arm 26.The four generally arcuate boundaries 38 of the blades as assembled tothe hub 22 define arcs of a circle having a diameter of about 120 mm ina fan blade assembly 16 having an overall diameter OD of about 354 mm(about fourteen inches). The relatively flat leading portions 34A of theblade inner portions 34 are not coplanar with each other when mounted tothe hub. They are instead slightly angled with respect to a verticalplane extending through the axis of rotation. When viewed along the axisof rotation of the fan blade assembly, there is a slight overlap of eachblade inner portion 34 with the inner portions 34 of adjoining blades.As shown in FIG. 2, the curved part 34B of the inner portion 34 of eachblade extends over a small relatively flat portion of an adjoining bladewhen the blade assembly is viewed from the front. A gap or passagebetween adjacent blades is defined in part by the suction side of thetrailing portion of one blade and the pressure side of the leadingportion of an adjacent blade. As the mean camber line of the blade 20transitions from more tangential to more axial, the air passage widthopens up and the average air velocity drops.

The portions of the blades extending radially outward from the innerportions 34 are curved, as shown in FIG. 4, such that the inner(suction) surfaces that face the motor are generally convex and theouter (pressure) surfaces are generally concave. The leading edge 40 ofeach blade is generally concave as viewed from the front or rear (FIG.5) while the trailing edge 42 is generally convex. The leading edge isgenerally forward swept, which contributes to the quiet operation of thefan blade assembly 14. The leading and trailing edges both have radiallyinner portions that extend rearwardly and radially outer portions thatextend forwardly (towards the direction of rotation), as shown in FIGS.2 and 3. The radially inner portions of the blades accordingly haverearward sweep while the radially outer portions have a forward sweep.The ratio of average blade chord to pitch (solidity) is about 0.4,preferably greater, and most preferably 0.405. The chord line of eachblade is fairly uniform, though it is slightly larger mid-span than neareither end.

The camber angle θ, as shown in FIG. 6, exceeds about twenty-twodegrees, and preferably is about 23 degrees. The camber angle does notvary significantly between the boundary 38 and the outer edge 46. FIG. 9shows the blade angle β distribution for various points on the bladefrom the leading edge 40 (0% M) to the trailing edge 42 (100% M) at adistance of 16% span 41 (i.e., 16% of the distance from the boundary 38to outer edge 46), 33% span 43 and at the outer edge 46. As shown inFIG. 6, the blade angle β for any particular point along the camber lineof a blade is the angle created by the intersection of the axis ofrotation 45 of the blade and the tangent to the camber line at thatparticular point.

Referring back to FIG. 5, the outer edge 46 of the blade has a radius ofcurvature of about 155 mm. Its length is substantially less than thelength of either the leading edge 40 or the trailing edge 42. Theforward swept angle α is greater than sixty degrees and is preferablyabout 61.2 degrees. In operation, it has been found that loading of theblade is nonuniform, and peaks near the leading edge in the area nearthe radially outer portion thereof and approximately mid-chord in thearea near the hub.

The outer portions 44 of the blades have outer pressure surfaces thatare generally concave between the leading and trailing edges 40, 42 aswell as between the boundaries 38 and the outer edges 46. As viewed fromthe side of the blade assembly, the leading edge 40 of each blade anglesrearwardly towards the electric motor and then forwardly. The camberline through the outer portion 44 of each blade is curved such that theleading portion thereof extends rearwardly with-respect to a planeextending perpendicularly through the axis of rotation. The trailingportion of the camber line extends forwardly with respect to this plane.The length L of each blade 20, as measured between inner and outer edgesalong a line extending through the two rivets 32, is about 157 mm. Thewidth W of each blade 20, as measured between a first line tangent tothe trailing edge 42 and a second parallel line running tangent to theoutermost part of the leading edge 40 is about 132 mm. The maximum depthD of each blade (FIG. 7) is about twenty-one millimeters (21 mm). Thelengths of the leading and trailing edges both substantially exceed thelength of the outer edge 46.

A fan blade assembly 14 made in accordance with the preferred embodimentdescribed above is capable of moving substantial volumes of air (e.g.about 450 cfm) quietly and efficiently. It will be appreciated that thefan blade assembly can be manufactured in different sizes and made fromdifferent materials. The assembly can be incorporated in fans other thanstand fans. The fan may be operated at different speeds and include anoscillation mechanism.

A fan blade assembly 114 according to a second embodiment of theinvention is shown in FIGS. 9 and 10. The assembly includes fiveidentical blades 120 that are secured to a central hub 122. The hub 122includes a generally hemispherical body. The rear side of the hubincludes five pairs of threaded openings (not shown) used for securingthe blades 120. It further includes a center opening 124, as shown inFIG. 11, for receiving the shaft of a motor (not shown).

Each blade 120 is preferably made from aluminum and has a substantiallyuniform thickness. In this embodiment, the thickness of the airfoilportion of the blade is about 1.5 mm. As discussed above with respect tothe first embodiment, the blade thickness can vary over a range withoutmaterially affecting performance. The blade includes an inner or rootportion 134 that may or may not have the same thickness as the airfoilportion of the blade. The inner portion includes a curved inner edge 136and a generally arcuate boundary 138 that separates the inner portion134 from the airfoil portion of the blade. The curvature of the boundary138 substantially matches the curvature of the hub 122. When mounted tothe hub, the inner portions 134 of the blades adjoin the rear surface ofthe hub. Openings 135 are aligned with the threaded openings in the hub.Screws 132 are employed to secure each blade to the hub. The boundaries138 adjoin the peripheral surface of the hub. In this embodiment, thediameter of the rear surface of the hub is about 114 mm while theoverall diameter OD of the fan blade assembly is about 394 mm. The depthDH of the hub is about 88.9 mm.

The blade 120 is generally “mid” loaded when in operation as opposed tofront or rear loaded. While there is a small peak near the leading edge,loading is relatively uniform throughout the blade when compared to theblade 20 described above. The forward swept angle a of the blade, asshown in FIG. 13, is greater than seventy degrees, and preferably about77.3 degrees. The blade has a length L of about 165 mm, a width W, asshown in FIG. 13, of about 144.3 mm, and a maximum depth D of about 46.6mm.

The mean camber angle θ, as shown in FIG. 15, is greater than thirteendegrees, preferably about 13.65 to 13.7 degrees. The camber angle variesapproximately from 7 degrees to 20 degrees. FIG. 16 shows the bladeangle β distribution for various points on the blade from the leadingedge 140 (0% M) to the trailing edge 142 (100% M) at the hub 138, at adistance of 10% span 141, 20% span 143, 45% span 145, 62% span 147, 75%span 149, 87% span 151, 90% span 153 and at the outer edge 146.

The leading edge 140 of the blade 120 is largely concave when viewedfrom the front or rear along the axis of rotation while the trailingedge 142 is generally convex. The leading edge 140 has a small convexportion 140 a near its inner (hub) end 138 while the trailing edge 142has slightly concave portions 142 a near its inner and outer ends. Thesolidity is about 0.6 or greater, preferably about 0.68. As shown inFIGS. 11 and 13, each blade 120 is rearward swept near the hub andforward swept from about the mid-span area of the airfoil to the outeredge 146. The width of the blade is greater near the outer edge thannear the hub. The blades overlap each other near the hub 122. Thecurvature of the camber line is greatest near the leading edge of theblade. The blade is also curved between the hub and outer edge such thatthe pressure surface is concave between these points.

The fan blade assembly 114 can be incorporated within a stand fan suchas shown in FIG. 1 or other type of portable electric fan intended forhome or office use.

1. A fan blade assembly for an electric axial flow fan comprising: ahub, and a plurality of fan blades mounted to the hub for providingaxial air flow as the hub is rotated in a direction about an axis ofrotation, each blade including: a blade body having an airfoil portionof substantially uniform thickness and including radially inner, outerand mid-span portions, a leading edge, a trailing edge, an outer edgeconnecting the leading and trailing edges and having a length that isshorter than the lengths of the leading and trailing edges, a pressuresurface, a suction surface, a curved mean camber line wherein thepressure surface is generally concave and the suction surface isgenerally convex between the leading and trailing edges, the leading andtrailing edges being curved such that the airfoil radially inner portionis rearward swept with respect to the direction of rotation of the huband the radially outer portion is forward swept with respect to thedirection of rotation of the hub about the axis, the pressure surfacebeing generally concave and the suction surface being generally convexbetween the hub and the outer edge.
 2. A fan blade assembly as describedin claim 1 wherein the blade body includes a mean camber angle exceedingtwent-two degrees.
 3. A fan blade assembly as described in claim 2wherein the leading edge defines a forward swept angle greater thansixty degrees.
 4. A fan blade assembly is described in claim 3 whereinthe ratio of blade chord to pitch is about 0.4 or greater.
 5. A fanblade assembly as described in claim 4 wherein the ratio of blade chordto pitch is about 0.4.
 6. A fan blade assembly as described in claim 4wherein the hub includes a plurality of radially outwardly extendingarms, a fan blade being secured to each arm.
 7. A fan blade assembly asdescribed in claim 1 wherein the mean camber line has a maximumcurvature near the trailing edge.
 8. A fan blade assembly as describedin claim 7 wherein the blade body has a mean camber angle of the airfoilportion greater than twenty-two degrees.
 9. A fan blade assembly asdescribed in claim 7 wherein the ratio of blade chord to pitch is about0.4 or greater.
 10. A fan blade assembly as described in claim 7 whereinthe leading edge defines a forward swept angle greater than sixtydegrees.
 11. A fan blade assembly as described in claim 7 wherein theblades are arranged on the hub and configured such that, when rotatedabout the axis of rotation, peak loading on the blade occurs near theleading edge of the outer and mid-span portions and away from theleading edge near the hub.
 12. A portable fan comprising: a support; anelectric motor mounted to the support; a fan blade assembly operativelyassociated with the electric motor; a grill at least partially enclosingthe fan blade assembly; and the fan blade assembly including a hub and aplurality of fan blades mounted to the hub, each blade including: ablade body having an airfoil portion of substantially uniform thicknessand including radially inner, outer and mid-span portions, a leadingedge, a trailing edge, an outer edge connecting the leading and trailingedges, a pressure surface, a suction surface, a curved mean camber linewherein the pressure surface is generally concave and the suctionsurface is generally convex between the leading and trailing edges, theleading and trailing edges being curved such that the airfoil radiallyinner portion is rearward swept with respect to the direction ofrotation of the hub and the radially outer portion is forward swept withrespect to the direction of rotation of the hub about the axis, thepressure surface being generally concave and the suction surface beinggenerally convex between the hub and the outer edge.
 13. A portable fanas described in claim 12 wherein the leading edge of each blade definesa forward swept angle greater than sixty degrees.
 14. A portable fan asdescribed in claim 12 wherein the ratio of blade chord to pitch is about0.4 or greater.
 15. A portable fan as described in claim 12 wherein themean camber line has a maximum curvature near the trailing edge.
 16. Aportable fan as described in claim 15 wherein the blade body has a meancamber angle which exceeds twenty two degrees.
 17. A portable fan asdescribed in claim 15 wherein the hub includes four radially outwardextending arms, a fan blade being secured to each arm.
 18. A portablefan as described in claim 12 wherein the blades are arranged on the huband configured such that, when rotated about the axis of rotation, peakloading on the blade occurs near the leading edge of the outer andmid-span portions and away from the leading edge at the inner portionnear the hub.
 19. A fan blade assembly for an axial flow electric fan,comprising: a hub, a plurality of fan blades mounted to the hub forproviding axial air flow as the hub is rotated in a direction about anaxis of rotation, each blade including: a blade body having an airfoilportion, a leading edge, a trailing edge, a pressure surface, a suctionsurface, a curved mean camber line wherein the pressure surface isgenerally concave and the suction surface is generally convex betweenthe leading and trailing edges, the leading edge and trailing edge beingcurved such that the airfoil portion includes a radially inner portionthat is rearward swept and a radially outer portion that is forwardswept with respect to the direction of rotation of the hub, and theratio of blade chord to pitch being about 0.6 or greater.
 20. A fanblade assembly as described in claim 19 wherein the airfoil portion ofeach blade has a substantially uniform thickness.
 21. A fan bladeassembly as described in claim 20 wherein five blades are mounted to thehub, each blade overlapping an adjoining blade near the hub.
 22. A fanblade assembly as described in claim 21 wherein the hub includes acircular edge, each blade including a root portion adjoining the airfoilportion and an arcuate boundary separating the root and airfoilportions, the root portion being secured to the hub, the arcuateboundary adjoining the circular edge of the hub.
 23. A fan bladeassembly as described in claim 21 wherein each blade has a mean camberangle of about 13.65 to 13.7 degrees and the solidity is about 0.68. 24.A fan blade assembly as described in claim 20 wherein the camber linehas a maximum curvature near the leading edge.